A simple method for quantifying specific mRNAs in small numbers of early mouse embryos

HOX genes are expressed in bovine and mouse oocytes and early embryos

HOX proteins are transcription factors that play a major role in patterning the body axis of vertebrates from the gastrulation stage. While nothing has been reported so far about their roles at earlier stages, there is evidence that some HOX genes are expressed before gastrulation. The objective of this work was to study the pattern of expression of several HOX genes during oocyte maturation and early embryonic development up to the blastocyst stage. Using nested PCR, HOXD1, HOXA3, HOXD4, HOXB7, HOXB9, and HOXC9 transcripts were detected in bovine oocytes and early embryos at various frequencies depending on the stage of development. Quantitative PCR was performed on bovine oocytes and early embryos: relative expression of HOXD1, HOXA3, and HOXC9 decreased sharply after the 5-8 cell stage. HOXB9 relative expression increased between the oocyte and the morula stage. All transcripts seemed to be of maternal origin before the maternal to embryonic transition, as demonstrated by blocking transcription with α-amanitin. Reverse transcription was performed with either hexamers or oligo-dT, allowing for the determination that HOXC9 transcripts were slightly deadenylated during oocyte maturation; HOXD1, HOXA3, and HOXB9 transcripts were not, indicating that they could be translated. Hoxd1, Hoxa3, Hoxb9, and Hoxc9 expression was also detected in mouse oocytes and early embryos. A similar pattern of expression was found in the two species. In conclusion, mammalian HOX genes might be implicated in the control of oocyte maturation, the maternal-to-embryonic transition or the first steps of embryo differentiation.

Standard-curve competitive RT-PCR quantification of myogenic regulatory factors in chicken embryos

The reverse transcription-polymerase chain reaction (RT-PCR) is the most sensitive method used to evaluate gene expression. Although many advances have been made since quantitative RT-PCR was first described, few reports deal with the mathematical bases of this technique. The aim of the present study was to develop and standardize a competitive PCR method using standard-curves to quantify transcripts of the myogenic regulatory factors MyoD, Myf-5, Myogenin and MRF4 in chicken embryos. Competitor cDNA molecules were constructed for each gene under study using deletion primers, which were designed to maintain the anchorage sites for the primers used to amplify target cDNAs. Standard-curves were prepared by co-amplification of different amounts of target cDNA with a constant amount of competitor. The content of specific mRNAs in embryo cDNAs was determined after PCR with a known amount of competitor and comparison to standard-curves. Transcripts of the housekeeping -actin gene were measured to normalize the results. As predicted by the model, most of the standard-curves showed a slope close to 1, while intercepts varied depending on the relative efficiency of competitor amplification. The sensitivity of the RT-PCR method permitted the detection of as few as 60 MyoD/Myf-5 molecules per reaction but approximately 600 molecules of MRF4/Myogenin mRNAS were necessary to produce a measurable signal. A coefficient of variation of 6 to 19% was estimated for the different genes analyzed (6 to 9 repetitions). The competitive RT-PCR assay described here is sensitive, precise and allows quantification of up to 9 transcripts from a single cDNA sample.

Multiple symmetric lipomatosis may be the consequence of defective noradrenergic modulation of proliferation and differentiation of brown fat cells

Multiple symmetric lipomatosis (MSL) is an inherited disorder in which enlarging and unencapsulated lipomas symmetrically develop in the subcutaneous tissue of the neck, shoulders, mammary, and truncal regions. In some cases, it is associated with mitochondrial DNA abnormalities. The pathogenesis of MSL is completely unknown, although the fat deposits may be due to a neoplastic-like proliferation of functionally defective brown adipocytes. It has recently been demonstrated that the beta(3)-adrenergic receptor is the functionally relevant adrenergic receptor subtype in brown adipocytes and that its stimulation by noradrenaline (NA) modulates the expression of genes, such as uncoupling protein (UCP)-1 and inducible nitric oxide synthase (iNOS), involved in fat cell proliferation and differentiation. Furthermore, Trp64Arg mutation of the beta(3)-adrenoceptor has been implicated in lower NA activity in adipose tissues. The aim of this study was to investigate the molecular and functional characteristics of MSL adipocytes and to analyse the effects of nitric oxide (NO) on the proliferation/differentiation of MSL adipocytes in culture, and the relevance of putative noradrenergic deficit in the development of lipomas in MSL patients. Cultured MSL adipocytes were able to synthesize UCP-1 (the selective marker of brown adipocytes), but unlike that of normally functioning brown fat cells, the expression of the UCP-1 gene was not significantly induced by NA. NA is also defective in inducing iNOS gene expression, thus leading to reduced NO production and a consequent reduction in the anti-proliferative, adipogenic (mitochondrial biogenesis) effects of NA on MSL cells. Furthermore, the transcriptional peroxisome proliferator-activated receptor gamma co-activator-1 (PGC-1), which plays a key role in the sympathetic-stimulated mitochondrial biogenesis of brown adipocytes, is expressed but not induced by NA in MSL cells, as it is in brown adipocytes. The study did not find any association between beta(3)-adrenoceptor gene polymorphism and noradrenergic signalling defects in MSL subjects with or without mitochondrial DNA mutations.

Gene expression in sexually dimorphic muscles in sheep

Testosterone is known to act differentially on skeletal muscle from different regions of the body. Two genes likely to mediate the testosterone effect are insulin-like growth factor I (IGF-I), an important growth regulator acting in an autocrine and paracrine way, and androgen receptor (AR), because receptor density could account for differential muscle growth. Another muscle-specific gene that may play a role in differential muscle growth is myostatin, a member of the transforming growth factor-beta superfamily, shown to be a negative regulator of skeletal muscle mass. The objective of this study was to quantify and compare the steady state expression of these three genes in two different skeletal muscles in sheep. Eleven Dorset rams were slaughtered after reaching puberty and total RNA was extracted from samples of semitendinosus and splenius muscles. Insulin-like growth factor I mRNA was measured using a competitive reverse-transcription-polymerase chain reaction. Androgen receptor and myostatin mRNA were measured by a ribonuclease protection assay (RPA) with standard curves. The means (attomoles/microg RNA) for splenius and semitendinosus muscles were 1.39 and 1.02 (SE = 0.14), 4.05 and 2.96 (SE = 0.24), and 4.30 and 3.85 (SE = 0.37) for IGF-I, AR, and myostatin, respectively. The difference between the two muscles was significant for IGF-I and AR mRNA levels with higher levels in the splenius but not significant for myostatin. Our results show that locally produced IGF-I and the regulation of AR expression may be important for sexually dimorphic muscle growth patterns.

Changes in FAT/CD36, UCP2, UCP3 and GLUT4 gene expression during lipid infusion in rat skeletal and heart muscle

OBJECTIVE

It has been reported that an increased availability of free fatty acids (NEFA) not only interferes with glucose utilization in insulin-dependent tissues, but may also result in an uncoupling effect of heart metabolism. We aimed therefore to investigate the effect of an increased availability of NEFA on gene expression of proteins involved in transmembrane fatty acid (FAT/CD36) and glucose (GLUT4) transport and of the uncoupling proteins UCP2 and 3 at the heart and skeletal muscle level.

STUDY DESIGN

Euglycemic hyperinsulinemic clamp was performed after 24 h Intralipid(R) plus heparin or saline infusion in lean Zucker rats. Skeletal and heart muscle glucose utilization was calculated by 2-deoxy-[1-(3)H]-D-glucose technique. Quantification of FAT/CD36, GLUT4, UCP2 and UCP3 mRNAs was obtained by Northern blot analysis or RT-PCR.

RESULTS

In Intralipid(R) plus heparin infused animals a significant decrease in insulin-mediated glucose uptake was observed both in the heart (22.62+/-2.04 vs 10.37+/-2.33 ng/mg/min; P<0.01) and in soleus muscle (13.46+/-1.53 vs 6.84+/-2.58 ng/mg/min; P<0.05). FAT/CD36 mRNA was significantly increased in skeletal muscle tissue (+117.4+/-16.3%, P<0.05), while no differences were found at the heart level in respect to saline infused rats. A clear decrease of GLUT4 mRNA was observed in both tissues. The 24 h infusion of fat emulsion resulted in a clear enhancement of UCP2 and UCP3 mRNA levels in the heart (99.5+/-15.3 and 80+/-4%) and in the skeletal muscle (291.5+/-24.7 and 146.9+/-12.7%).

CONCLUSIONS

As a result of the increased availability of NEFA, FAT/CD36 gene expression increases in skeletal muscle, but not at the heart level. The augmented lipid fuel supply is responsible for the depression of insulin-mediated glucose transport and for the increase of UCP2 and 3 gene expression in both skeletal and heart muscle.

Differential priming of RNA templates during cDNA synthesis markedly affects both accuracy and reproducibility of quantitative competitive reverse-transcriptase PCR

Quantitative competitive reverse-transcriptase PCR is the most sensitive method for studying gene expression. To investigate whether the accuracy of the calculated target mRNA copy number is affected by the cDNA priming process, we utilized primers of different lengths, concentrations and primer sequences to prime cDNA synthesis reactions. Our results show a approximately 19-fold increase in the calculated mRNA copy number from cDNA synthesis reactions primed with random hexamers (P<0.001, n=4), and a approximately 4-fold increase in copy number with a specific hexamer (P<0.001, n=4) compared with that obtained with a 22-mer-sequence-specific primer. The increase in calculated mRNA copy number obtained by priming cDNA synthesis with the shorter specific and non-specific primers could be explained largely by the synthesis of truncated standard cDNA molecules lacking a requisite binding site for amplification with PCR primers. Since these truncated standard cDNA molecules could not be amplified and standard RNA is used to quantify target mRNA copy number, this phenomenon resulted in overestimation of target mRNA copy number. In conclusion, accurate determination of target mRNA copy number is most likely if a long specific antisense primer is used to prime cDNA synthesis.

Role of sympathetic activity in controlling the expression of vascular endothelial growth factor in brown fat cells of lean and genetically obese rats

The thermogenic activity of brown adipose tissue (BAT) is heavily dependent on high perfusion, through its dense vascular system. Angiogenesis must go hand-in-hand with BAT functions, but little is known about the factors controlling it. In the present study we demonstrate that: (a) vascular endothelial growth factor (VEGF) is synthesised and released in brown adipocytes in culture; (b) VEGF mRNA isoforms and protein appear in dispersed mature brown adipocytes and whole tissue; (c) VEGF expression is increased in BAT from cold-exposed rats, and in cultured brown adipocytes exposed to noradrenaline and the beta3-adrenoceptor agonists; (e) BAT from genetically obese (falfa) rats exhibits reduced expression of VEGF as well as a change in the ratio of mRNA isoforms. It is concluded that sympathetic control of VEGF expression via noradrenaline acting on beta3-adrenoceptors plays a major role in developmental and adaptive angiogenesis, and defects in this contribute to the reduced thermogenic capacity of BAT in genetic obesity.

Effects of nitric oxide on proliferation and differentiation of rat brown adipocytes in primary cultures

1. In the present work, we study the effect of NO on the proliferation and differentiation of brown fat cells in primary cultures. 2. Brown fat precursor cells isolated from rat brown adipose tissue were cultured for 8 days until confluence and treated daily with the NO donating agents, S-nitroso-acetyl penicillamine (SNAP) or S-nitroso-L-glutathione (GSNO). Both agents (300 microM) decreased cell proliferation approximately 8 fold on day 8. The inhibitory effect of NO was unlikely to be due to cytotoxicity since (i) cells never completely lost their proliferation capacity even after 8 days of exposure to repeated additions of SNAP or GSNO, and (ii) the inhibitory effect was reversible after removal of the media containing NO donors. 3. Daily treatment with nitric oxide synthase inhibitors, such as NG-nitro-L-arginine methyl ester (L-NAME, 300 microM), led to the stimulation of cell proliferation by 44+/-5%, n=3, suggesting that NO, endogenously produced in brown adipocytes, may be involved in modulating cell growth. 4. Daily treatment with both SNAP or GSNO induced significant mitochondriogenesis, measured as the mitochondrial conversion of 3-[4,5-dimethylthiazol-2-yl-]-2,5-diphenyl tetrazolium bromide (MTT) to formazan, whilst daily treatment with L-NAME was without effect. 5. The inhibition of cell proliferation by NO donors was accompanied by the expression of two genes coding for peroxisome proliferator activated receptor-gamma and uncoupling protein-1, which are upregulated during differentiation. 6. Increasing cyclic GMP in cells by 8-bromo-cyclic GMP (100-1000 microM) did not reproduce the observed NO effects on either cell number or gene expression. On the other hand, chronic treatment with the inhibitor of the NO-stimulated guanylyl cyclase, 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ), reduced the expression of peroxisome proliferator activated receptor-gamma and uncoupling protein-1.

SR59230A blocks beta3-adrenoceptor-linked modulation of upcoupling protein-1 and leptin in rat brown adipocytes

Experimental evidence suggests that, by stimulating energy expenditure in brown fat, selective beta3-adrenoceptor agonists can reduce body weight in obese rodents. In order to investigate further the physiological role of beta3-adrenoceptors in brown adipocytes, we analysed the effects of selective beta3-adrenoceptor agonists and antagonists on uncoupling protein-1 and leptin gene expression in culture-differentiated brown fat cells. Our main findings were that: (i) the leptin gene is expressed in brown adipocytes; (ii) the selective beta3-adrenoceptor agonist, N[(2S)-7-carbethoxy-1,2,3,4-tetrahydronaphth-2-yl]-(2R)-2-hydroxy- 2-(3-chlorophenil)ethanamine hydrochloride (SR58611A), inhibits leptin gene while inducing uncoupling protein-1 gene expression; (iii) these opposite effects of SR58611A are antagonized by the selective beta3-adrenoceptor antagonist, SS-enantiomer 3-(2-ethylphenoxy)-1-(1S),2,3,4-tetrahydronaphth-1-ylamin ol]-(2S)-2-propanol oxalate (SR59230A), but not by the selective beta1-adrenoceptor antagonist (+/-)-[2-(3-carbamoyl-4-hydroxyphenoxy)-ethylamino]-3-[4(1-methyl- 4-trifluoromethyl-2-imidazolyl)-phenoxy]-2 propanol (CGP20712A); and (iv) these effects are due to increased cyclic AMP levels. These results confirm by means of a different experimental approach that beta3-adrenoceptors play a central role in controlling the expression of genes that are important for brown fat function.

Characterization of gene expression in mouse blastocyst using single-pass sequencing of 3995 clones

To study the gene expression profile in the mouse blastocyst and to identify embryonic stage-specific genes, we randomly selected cDNAs derived from mouse blastocysts and sequenced a total of 3995 clones from one or both ends. Excluding the uninformative clones, 3395 clones were grouped as 937 different kinds of genes. Among these, 465 and 406 species showed similarity to known genes and expressed sequence tags (ESTs), respectively, whereas 66 species showed no significant similarity to any genes in known databases. Analysis of these cDNAs revealed that this library contained a variety of functional genes as well as genes that have not been detected in the human EST database; it should provide us with a useful resource for molecular analysis of developmental mechanisms. Although the human EST project is considered to represent roughly half of all genes, our findings indicate that many early stage developmental genes remain to be identified.

Relevance of the D13 region to the function of the skeletal muscle chloride channel, ClC-1

Although hydropathy analysis of the skeletal muscle chloride channel protein, ClC-1, initially predicted 13 potential membrane spanning domains (D1 to D13), later topological studies have suggested that domain D4 is extracellular and that D13, conserved in all eukaryotic ClC channels, is located within the extensive cytoplasmic tail that makes up the carboxyl terminus of the protein. We have examined the effect of deleting D13 (DeltaD13) and the function of the carboxyl tail by removing the final 72 (fs923X), 100 (fs895X), 125 (L869X), 398 (N596X), and 420 (Q574X) amino acids from rat ClC-1. Appropriate cDNA constructs were prepared and expressed using the baculovirus Sf9 insect cell system. Patch clamp analysis of chloride currents in Sf9 cells showed that only relatively insubstantial changes could be attributed to the expressed fs923X, fs895X, and DeltaD13 mutants compared with wild type rat ClC-1. For N596X and Q574X, however, adequate mRNA could be detected, but neither patch clamp nor polyacrylamide gel electrophoresis showed corresponding protein production. By contrast, expression of L869X was demonstrable by polyacrylamide gel electrophoresis, but no chloride conductance attributable to it could be detected. Overall, our results indicate that the domain D13 is dispensable, as are the final 100 amino acids, but not the final 125 amino acids or more, of the carboxyl tail. Some essential region of unknown significance, therefore, appears to reside in the 18 amino acids after D13, from Lys877 to Arg894.

Analysis of variation in relative mRNA abundance for specific gene transcripts in single bovine oocytes and early embryos

Variation in the abundance of a specific gene transcript was assessed in single bovine oocytes and in vitro-derived blastocysts. Transcripts encoding the Na+,K(+)-ATPase alpha 1 subunit were detected by reverse-transcription polymerase chain reaction (RT-PCR) and quantified relative to an exogenously supplied rabbit alpha-globin mRNA using laser-induced fluorescence capillary electrophoresis (LIF-CE). The precision of this relative abundance (RA) calculation was predicted and shown to resolve 2-fold differences in transcript abundance between individual blastocysts and predicted in oocytes to resolve 3-fold differences. The RA of the alpha 1 subunit transcript differed by 2- to 3-fold among blastocysts, and 3- to 6-fold among oocytes. Comparison of a general population of oocytes with blastocysts revealed little overlap in RA values between the two groups, with a 8- to 14-fold increase in the mean RA for each group with development observed in two successive experiments (P < or = 0.05). In contrast, oocytes selected for their developmental competence on the basis of morphologic criteria exhibited only a 1.6- to 1.7-fold developmental increase when the assay was performed on cDNA generated from either embryo pools (n = 6 versus 6) or individuals (n = 7 versus 7), respectively. These results provide the first characterization of the degree of heterogeneity in the abundance of a specific mRNA transcript among individual mammalian oocytes and preimplantation embryos and demonstrate that transcript relative abundance can be correlated with bovine oocyte morphology.

Quantification of Coxiella burnetii by polymerase chain reaction (PCR) and a colorimetric microtiter plate hybridization assay (CMHA)

A colorimetric microtiter plate hybridization assay (CMHA) for the quantitative determination of Coxiella burnetii DNA after amplification by externally controlled polymerase chain reaction (PCR) is described. The quantification assay is based on an enzyme linked immunosorbent assay (ELISA) format. Cloned DNA, representing a sequence complementary to an internal part of the diagnostic amplicon, was noncovalently attached to the wells of a microtiter plate. Biotinylated PCR product was hybridized to the immobilized capture probe. Bound product was detected via streptavidin horse-radish peroxidase. The devised nonisotopic technique allows specific, rapid, and convenient quantification of C. burnetii DNA. Additionally, it is compatible with standard laboratory ELISA equipment, making this assay amenable to automation and permitting processing of large sample numbers.

Expression of collagens I, III, IV and V mRNA in excimer wounded rat cornea: analysis by semi-quantitative PCR

A semi-quantitative polymerase chain reaction (PCR) methodology was used to evaluate the kinetic changes occurring in collagens I, III, IV and V mRNA in rat cornea following excimer laser keratectomy. cDNA was synthesized from RNA extracted from rat cornea at various times following excimer laser photoablative keratectomy. Collagen cDNA sequences were subsequently amplified using specific sets of oligonucleotide primers. Competitive PCR amplification was carried out using an internal standard so that a semi-quantitative analysis of message for synthesis of collagen types I, III, IV and V could be performed and time course dynamics of message for these collagens studied. There was a biphasic increase in the levels of collagens III, IV and V mRNA following excimer laser keratectomy. Collagen I mRNA levels demonstrated a more sustained increase and were still elevated at 6 weeks following wounding. Collagens IV and V mRNA showed the largest increase with an approximate three fold increase over controls between 4 days and 1 week. Our results demonstrate that upregulation of stromal collagens I, III, and V mRNA and basement membrane collagen IV mRNA occurs in rat cornea following excimer laser keratectomy.

A rapid method for mRNA detection in single-cell biopsies from preimplantation-stage bovine embryos

Major questions concerning the control of development and gene expression at the cellular level are still unanswered. Nowhere is this more evident than during the earliest stages of development and embryogenesis. This study describes the detection of specific gene transcripts in single cells derived from bovine embryos. Following in vitro fertilization (IVF) and in vitro culture (IVC) of bovine embryos, small groups of cells and even single blastomeres from 32 to 64-cell embryos were micromanipulated into individual tubes for analysis of cytoplasmic RNAs. Reverse transcriptase-PCR was applied to cell lysates for the amplification of beta-actin mRNA transcripts. Primers were designed to flank an intron expected to be present within genomic DNA sequences, thus allowing for simple differentiation between DNA- and RNA-derived amplification products. Using a 50-cycle amplification profile, a 260 bp band could be seen as a PCR product derived from a single blastomere following electrophoresis in an ethidium bromide-stained agarose gel. The identity of the band was verified by DNA sequence determination and diagnostic restriction digestion. Lysates derived from single blastomeres in this way have been used for simultaneously phenotyping multiple RNA products. This capability allows the spatial analysis of gene expression and development within embryos from the earliest stages of cellular differentiation.

Comparative sequence analysis of the human and pufferfish Huntington's disease genes

The Huntington's disease (HD) gene encodes a novel protein with as yet no known function. In order to identify the functionally important domains of this protein, we have cloned and sequenced the homologue of the HD gene in the pufferfish, Fugu rubripes. The Fugu HD gene spans only 23 kb of genomic DNA, compared to the 170 kb human gene, and yet all 67 exons are conserved. The first coding exon, the site of the disease-causing triplet repeat, is highly conserved. However, the glutamine repeat in Fugu consists of just four residues. We also show that gene order may be conserved over longer stretches of the two genomes. Our work describes a detailed example of sequence comparison between human and Fugu, and illustrates the power of the pufferfish genome as a model system in the analysis of human genes.

Expression of the mouse testis-determining gene Sry in male preimplantation embryos

The testis-determining factor in the mouse is encoded by the Sry gene on the Y chromosome. Transcripts of this gene have been shown previously to be present in the genital ridge at the beginning of gonadal differentiation (11.5 days post coitum) and in adult testis. In this study, RNA transcripts of the Sry gene are also detected in male blastocyst-stage embryos (3.5 days post coitum) at approximately 40-100 copies per cell, long before overt sex differentiation. These results indicate that preimplantation mouse embryos have sexually dimorphic gene expression at least with respect to Sry transcripts. In addition, at least some of the Sry RNA transcripts in blastocysts are circular, as has been reported for Sry transcripts from adult testis. The appearance of Sry transcripts in blastocysts at this level raises the possibility that sex determination begins earlier during embryonic development than previously thought.

Expression of SGP-1 mRNA in preimplantation mouse embryos

In a search for genes expressed in preimplantation mouse embryos that are important for the earliest steps in differentiation, we identified an abundant mRNA that codes for a sulfated glycoprotein, SGP-1. The amount of this RNA rises approximately 100-fold during preimplantation development to a level approximately equal to that of beta-actin mRNA in blastocysts, although the level of these transcripts per cell remains fairly constant during these stages at approximately 2,000-4,000 copies. An antisense RNA that is complementary to approximately the last one-third of the message and contains an open reading frame of 455 nt was found in blastocysts at a 2-3-fold higher level than the mRNA. In situ hybridization with sense and antisense riboprobes showed that both strands are distributed throughout the embryo. The abundance of the SGP-1 mRNA indicates that the encoded protein may play an important role in the development of embryos, and the excess of antisense RNA raises the possibility of an unusual mechanism of regulating its expression.

Quantitation of bovine TNF-alpha mRNA by reverse transcription and competitive polymerase chain reaction amplification

A reverse transcription (RT) and competitive polymerase chain reaction (PCR) amplification technique was developed to quantify bovine tumor necrosis factor-alpha (TNF-alpha) mRNA. A bovine TNF-alpha cDNA insert containing plasmid was used to produce a 237-bp cDNA competitive template which, when PCR-amplified with primers designed to amplify bovine TNF-alpha cDNA, resulted in a 147-bp product distinguishable by agarose gel electrophoresis from the 378-bp TNF-alpha RT-PCR-amplified cDNA product. Dilutions of competitive template were co-amplified with constant amounts of total cellular RNA harvested from bovine alveolar macrophages (BAM). Products were separated in ethidium-bromide-stained agarose gels and relative amounts of TNF-alpha mRNA were determined by densitometric scanning of TNF-alpha cDNA and competitive template product bands on photographic negatives. Digestions with Pvu II and Sty I restriction endonucleases verified that RT-PCR-amplified TNF-alpha cDNA products were authentic. A time study indicated that TNF-alpha mRNA concentrations peaked 3 h after endotoxin and virus induction of BAMs.

Dopamine D2, D3, and D4 receptor mRNA levels in rat brain and pituitary during aging

Reverse Transcriptase-Polymerase Chain Reaction technique was used to determine the levels of the mRNAs encoding different receptors belonging to the D2 family in various brain areas of 6-, 12-, 18-, and 24-month-old rats. We found a progressive, age-dependent reduction in the mRNA levels of D2 short and D2 long receptors in corpus striatum, substantia nigra, and frontal cortex. D2 short and D2 long receptor mRNA levels were unchanged in hippocampus and olfactory tubercle, while they increased in pituitary. D3 receptor mRNA levels were reduced in olfactory tubercle and unchanged in striatum. D4 receptor mRNA levels were unmodified in pituitary gland. These data suggest that the molecular mechanisms responsible for regulating the pattern of expression of the various dopamine receptors are differentially regulated by aging.

Antisense strategy unravels a dopamine receptor distinct from the D2 subtype, uncoupled with adenylyl cyclase, inhibiting prolactin release from rat pituitary cells

The antisense strategy was used to unravel the functional contribution of the mRNAs encoding dopamine (DA) receptors to the multiple transduction mechanisms operated by DA in rat pituitary cells. An antisense oligonucleotide was designed to recognize seven nucleotides upstream and 11 nucleotides downstream from the initiation translation codon of the mRNA that encodes the DA D2 receptor. Addition of the antisense oligonucleotide for 7 days to primary culture of rat pituitary cells resulted in a decreased expression of DA D2 receptor as shown by (a) the virtual disappearance of [3H]spiroperidol binding sites and (b) the marked reduction in the levels of both the long and the short splice variant of the D2 receptor mRNAs. After this treatment, the DA D2 receptor agonist bromocriptine lost its capability both to inhibit adenylyl cyclase activity and to reduce prolactin mRNA levels. On the contrary, the inhibition of prolactin release induced by bromocriptine was affected minimally by the antisense oligonucleotide treatment. These data indicate that (a) translation of the mRNA encoding DA D2 receptors results in receptors that are negatively coupled with adenylyl cyclase and functionally linked to inhibition of prolactin synthesis; and (b) the release of prolactin might be regulated, at least in part, by a DA receptor that is encoded by mRNA species distinct from those encoding the D2 receptor.

Expression patterns of novel genes during mouse preimplantation embryogenesis

Little is known about the repertoire of genes expressed following zygotic gene activation, which occurs during the two-cell stage in the mouse. As an initial attempt to isolate novel genes, we used previously prepared two-cell and two-cell subtraction cDNA libraries (Rothstein et al., Genes Dev 6:1190-1201, 1992) to isolate a panel of seven cDNA clones. Three cDNAs had no match in the current DNA sequence data banks and three others revealed sequence homology to portions of sequences in the data banks. One cDNA was 90% homologous to the ras-related gene Krev/rap 1A. The temporal patterns of expression of these genes during oocyte maturation and preimplantation development were analyzed by a reverse transcription-polymerase chain reaction (RT-PCR) assay developed to measure relative levels of mRNAs. Three distinct temporal patterns of expression, designated Classes 1-3, were found. The two Class 1 genes displayed an actin-like pattern, with a gradual decline in expression during oocyte maturation and through the two-cell stage, followed by increases at the eight-cell and/or blastocyst stages. The four genes in Class 2 were expressed at relatively high levels during oocyte maturation and through the one-cell stage and then declined abruptly between the one- and two-cell stages; an increase then occurred at the eight-cell and/or blastocyst stages. The expression of the gene in Class 3 declined during oocyte maturation, but then showed a transient increase at the one-cell stage, with only a very slight increase in synthesis at either the eight-cell or blastocyst stage.

Quantitative measurement of calretinin and beta-actin mRNA [correction of mRNAIN] in rat brain micropunches without prior isolation of RNA

A microdissection technique for quantitation of neurochemicals in discrete brain nuclei has been applied to quantitative measurement of mRNA. The method permits quantitation of low abundance mRNA from submilligram amounts of tissue (10-500 micrograms protein). Discrete nuclei and other regions of the brain are solubilized in concentrated guanidine thiocyanate solution, mRNA is directly hybridized with riboprobes, and detected with a ribonuclease protection assay. This method eliminates the necessity for RNA isolation from solid tissue. No assumptions regarding RNA recovery are necessary since tissue specimens are solubilized, hybridized and treated with ribonuclease in a single tube. We have determined the mRNA levels of calretinin, a predominantly neuron-specific calcium binding protein in microdissected nuclei and other regions of rat brain. For interassay comparison, measurement of sample protein and beta-actin mRNA permits normalization and quantitation in terms of these internal controls. The quantity of calretinin mRNA ranged from 281 +/- 35 fg/micrograms protein in the thalamic paraventricular nucleus to 2.3 +/- 0.5 fg/micrograms protein for the cerebral cortex. The calretinin/beta-actin ratios ranged from 79.9 +/- 9.3% to 1.3 +/- 0.1%, respectively. The combination of microdissection techniques with a lysate RNase protection assay: (1) establishes this technique as quantitative for detection of high and low abundance mRNAs from microdissected brain specimens; (2) bypasses the inefficiencies and uncertainties associated with isolating RNA; and (3) enables large numbers of determinations from discrete brain nuclei to be analyzed in 2 to 3 days.

Isolation and expression of human 1,25-dihydroxyvitamin D3 24-hydroxylase cDNA

Human 1,25-dihydroxyvitamin D3 24-hydroxylase cDNA clones were isolated from an HL-60 cell cDNA library by using a reverse transcription/polymerase chain reaction-generated human cDNA probe. The 24-hydroxylase cDNA consists of a 1539-bp open reading frame encoding a 513-amino acid polypeptide. Protein sequence analysis shows that the human 24-hydroxylase is 90% homologous (82% identical) to that of the rat, with 100% homology in the 21-amino acid heme-binding region. Northern blot analysis showed that the 24-hydroxylase cDNA probe hybridized to a 3.4-kb mRNA species. Treatment of HL-60 cells with 0.1 microM 1,25-dihydroxyvitamin D3 for 24 hr produced a 30-fold increase in the 24-hydroxylase mRNA level. This result is consistent with previous studies in the same cell line, in which 24-hydroxylase activity was elevated to a maximum in 24 hr by a similar treatment with 1,25-dihydroxyvitamin D3. To verify the identity of these isolated cDNA clones, two polymerase chain reaction-amplified human 24-hydroxylase cDNA fragments containing the entire coding region were used to produce 24-hydroxylase enzyme activity in two genetic expression systems. Transient levels of 24-hydroxylase activity were measured in transfected mammalian COS-1 cells and in recombinant baculovirus-infected Spodoptera frugiperda (Sf21) insect cells.

A yeast artificial chromosome covering the tyrosinase gene confers copy number-dependent expression in transgenic mice

Expression of transgenes in mice often fails to follow the normal temporal and spatial pattern and to reach the same level as the endogenous copies. Only in exceptional cases has position-independent and copy number-dependent expression been reproduced. The size constraint of standard constructs may prevent the inclusion of important remote regulatory elements. Yeast artificial chromosomes (YACs) provide a means of cloning large DNA fragments and the transfer of YAC DNA into somatic cells has been reported. We have previously produced transgenic mice carrying a 35 kilobase YAC construct. Here we report the transfer of a 250 kilobase YAC covering the mouse tyrosinase gene into mice by pronuclear injection of gel-purified YAC DNA. The YAC was inserted into the mouse genome without major rearrangements and expression of the YAC-borne tyrosinase gene resulted in complete rescue of the albino phenotype of the recipient mice. Expression from the transgene reached levels comparable to that of the endogenous gene and showed copy number dependence and position independence.

Expression of the epidermal growth factor receptor gene is regulated in mouse blastocysts during delayed implantation

The delayed implantation model was used to study epidermal growth factor receptor(s) (EGF-R) in the mouse blastocyst. Delayed implantation and blastocyst dormancy were induced by ovariectomy on day 4 of pregnancy and were maintained by daily (days 5-7) injections of progesterone (P4). Blastocyst activation and implantation were initiated by coinjection of estradiol-17 beta (E2) with P4 on the 3rd day of delay. Immunostaining of EGF-R, autoradiographic detection of 125I-labeled EGF binding, and measurement of EGF-inducible subcellular protein tyrosine phosphorylation demonstrated the loss of EGF-R from blastocysts (dormant) recovered 24 h after ovariectomy or on the 3rd day of P4-maintained delay. However, increased EGF-R levels were detected in blastocysts (activated) recovered 12 or 24 h after E2 injection. Blastocyst EGF-R mRNA levels were quantitated by reverse transcriptase (RT)-PCR and distribution of this mRNA was examined by in situ hybridization. To provide a homologous probe for these studies, a mouse EGF-R partial cDNA was cloned and used as the template for synthesis of antisense- and sense-strand EGF-R RNA. Quantitative RT-PCR demonstrated an 8- to 10-fold reduction in EGF-R mRNA copies per cell in dormant blastocysts. In contrast, an 8-fold increase in EGF-R mRNA copies per cell was detected in activated blastocysts 8 h after injection of E2. In situ hybridization detected EGF-R mRNA in most cells of normal day 4 blastocysts but not in those of dormant blastocysts. These studies establish that expression of the EGF-R gene in mouse blastocysts is tightly regulated by maternal steroid hormonal status.

The use of reverse transcriptase-polymerase chain reaction (RT-PCR) to investigate specific gene expression in multidrug-resistant cells

Expression of specific genes at the level of mRNA can be studied using techniques such as Northern blot, slot/dot blot, RNase protection assay, in situ hybridisation and RT-PCR. In this article these methods of analysis are compared; RT-PCR offers higher levels of specificity and sensitivity than traditional methods of RNA analysis and as such has become the method of choice for the study of gene expression. The RT-PCR technique is described in detail with sections dealing with RNA extraction, choice of primers (including the use of cDNA sequence data bases), PCR and RT-PCR protocols in addition to the limitations of the method. The study of one particular mRNA transcript (MDR1) using RT-PCR is discussed in detail. Recently described methods for quantitation of PCR products are discussed. Quantitative PCR would appear to offer a method of studying gene expression in a more extensive way than has been possible to date.

Expression of the chlorophyll-a/b-protein multigene family in pea (Pisum sativum L.) : Evidence for distinct developmental responses

To measure transcript levels for individual members of the Cab (chlorophyll a/b protein) multigene family in pea under a range of developmental situations, we developed a system using cDNA synthesis, the polymerase chain reaction (PCR), and chemiluminescence detection. In order to design gene-specific PCR primers for all genes, a partial genomic clone for a fifth, Type I LHCII (light-harvesting complex of photosystem II) gene, Cab-9 The Cab-9 sequence appears in the Genbank/EMBL databases under the accession number M86906 , was isolated and sequenced. All seven known Cab genes in pea are expressed in light-grown buds and leaves, including several genes previously known only from genomic clones. There appear to be at least two groups of Cab genes in pea which differ in their response to light and development. The first group (consisting of Cab-8, AB96, Cab-215 and Cab-315) includes Type I, Type II and Type III genes, shows a relatively strong response to red light, and has bud transcript levels similar to or slightly higher than leaves. The second group, consisting of the Type I genes Cab-9, AB80 and AB66, shows little or no transcript accumulation 24 h after a red light pulse, and has higher transcript levels in leaves than in buds. Transcript levels for genes in this second group appear to be lower than those of the first group in all developmental situations examined. These data indicate that there has been an evolutionary divergence of the responses to light and development among the Type I LHCII genes.

The polymerase chain reaction and its potential role in clinical diagnostics and research

In-vitro amplification of deoxyribonucleic acid molecules by means of the polymerase chain reaction (PCR) must be regarded as the most important advance in the life sciences to take place during the last decade. Originally applied to the identification of mutations in well-known and fully sequenced human genes, its applications have now been extended to a wide variety of biological and medical disciplines, accompanied by significant technical improvements and sophisticated variations of the basic principle. Specialized molecular genetics laboratories were the first to employ this new method, and they still are in the process of extending its potential. Due to its unique properties, applications of PCR quickly spread to other areas of research, and numerous clinical studies have already employed PCR. The field is currently still expanding rapidly.

Molecular approaches for analyzing differential gene expression: differential cDNA library construction and screening

Complementary deoxyribonucleic acid (cDNA) libraries can be used as a means to isolate and identify cell-specific messenger ribonucleic acid (mRNA) sequences. The basic elements of cDNA library construction and screening are reviewed in the context of analyzing differentially expressed mRNAs. A brief overview of the recombinant DNA systems applied to cDNA library construction and the principles of screening cDNA libraries by plaque hybridization are provided. Methods for comparing mRNA populations by differential screening and by competition hybridization are discussed, and methods for constructing subtracted cDNA libraries, enriched in differentially expressed sequences, are presented. Also reviewed are the analysis of differentially expressed cDNAs by Southern and Northern hybridization, RNase protection, polymerase chain reaction, and sequencing.